Understanding "Endangered Species"
When we hear the term "endangered species," we mostly just think of rare creatures. However, "endangered species" implies more than that. It implies that the entire species is in danger of being wiped out. When a species is wiped out, it is considered extinct. The biggest causes of endangered species are the introduction of exotic species, like predator animals that the native animals haven't adapted for, and habitat change, such as deforestation or climate change.
Enjoyment
One of the most important reasons for conservation and protection of endangered species is the enjoyment of said species in future generations. If a species goes extinct today, you may have been able to see it, but your kids won't. Their kids won't ever see them either. We are members of a family of animals on this earth, and seeing a species go extinct is like losing a loved one. Sure, we'll get over it, but it's not something we shouldn't try to stop.
Ecology
As humans, we gaze down on the rest of the animal kingdom. We are certainly masters of our domain, yet that doesn't mean we shouldn't see through the eyes of those beneath us. Other animals share complex hierarchies and food chains. If you remove a link from that chain, you risk the whole thing falling apart. When a species goes extinct, we risk the overpopulation of their prey and the possible extinction of their predators.
Medicine
When we hear "endangered species," most of us don't think of plants. However, there are a great many species of plants also in danger of becoming extinct. Many of these plants carry medicinal properties that are in use or waiting to be discovered. Plants, especially endangered ones, are finding uses in even the most dire diseases, like cancer and AIDS. Certain animals, especially toxic ones, can also serve medicinal purposes, such as in anesthesia.
Agriculture
Though we don't often associate endangerment and agriculture, the two are invariably separated, especially as we look to the future. Certain endangered plants possess the ability to grow in soil and on land that we can't grow normal crops. As the human population climbs, we are going to run short of places to grow crops, or encounter problems we haven't faced before. It is important to conserve these plant species to ensure that the world doesn't go hungry in the future.